1. Field of the Invention
The present invention relates to an image forming apparatus including a function that utilizes a specified area of a recording sheet, on which an image has been formed, as an active portion; and in particular to an image forming apparatus including a function that generates a product by cutting a recording sheet; and to a control method for controlling the function.
2. Description of the Related Art
A conventional image forming apparatus performs heat fixing by, with use of a fixing roller, pressing a toner image that has been transferred onto a recording sheet. In the case of performing printing on both small and large recording sheets, control of the image forming apparatus is required as will be discussed below. For example, as shown in FIG. 43, when small recording sheets are fed in succession, the temperature becomes non-uniform between the center and ends of the fixing roller. When a large recording is fed thereafter, differences in image density occur and a fixing offset (i.e. a non-uniformity in the fixing of the toner image) occurs. FIG. 43 is a diagram showing a fixing temperature distribution after recording sheet (paper) feeding. In FIG. 43, the horizontal axis indicates position on the fixing roller, and the vertical axis indicates the fixing temperature.
As an example of a countermeasure, Japanese Patent Laid-Open No. H08-234620 proposes a low-cost, general method in which the printing operation is temporarily stopped, and fixing adjustment is performed until the temperature of the fixing roller has stabilized. When using the technique disclosed in Japanese Patent Laid-Open No. H08-234620, it is necessary to adjust the temperature of the fixing roller with use of a fixing heater having different light distribution characteristics as shown in FIG. 44. FIG. 44 is a diagram for illustrating the light distribution characteristics of a fixing heater. In FIG. 44, the horizontal axis indicates position on the fixing roller, and the vertical axis indicates the light distribution characteristics.
Also, as shown in FIG. 45, when recording sheets having a large sheet thickness (i.e. are thick) are fed in succession, the end portions of the recording sheets create small flaws (e.g. dents) on the surface of the fixing roller. It is known that when a large recording sheet is fed thereafter, these flawed portions cause small marks to appear in the image on the large recording sheet. FIG. 45 is a diagram showing a condition in which such flaws appear at end portions of thick paper. As a countermeasure, Japanese Patent Laid-Open No. H09-080956 proposes a method of removing flaws from the surface of the fixing roller.
Such fixing temperature adjustment and flaw removal are essential for maintaining image quality, but on the other hand, they are also the cause of a drop in productivity since printing operation is temporarily paused during the fixing temperature adjustment and flaw removal.
With an image forming apparatus such as a copy machine, it is possible to manipulate recording sheets having images formed thereon by connecting a post-processing apparatus to the image forming apparatus. For example, Japanese Patent Laid-Open No. 2005-104063 proposes an image forming apparatus that is configured to perform bookbinding processing by attaching thereto a function for gluing the edge of a paper bundle composed of a plurality of sheets of paper, and a cutting function for cutting sides other than the glued side.
However, the conventional technology described above has the following problems. For example, in the case of performing printing on both small recording sheets and large recording sheets, when there are many switches between small and large recording sheets in the same job, the job has to be paused at each switch in order to perform fixing temperature adjustment and flaw removal.
The following is a more specific description with reference to FIG. 46. FIG. 46 is a diagram showing timings at which fixing adjustment is performed in a job that utilizes different paper sizes. In FIG. 46, the case of performing bookbinding processing with use of an inner sheet bundle and a cover sheet that are different sizes is envisioned. For example, in the envisioned job, a bound book is created by collecting and bundling a plurality of small recording sheets, and then placing a large cover sheet around the bundle. As shown in FIG. 46, in such a case, there is the problem that productivity drops significantly due to the need to perform fixing temperature adjustment and flaw removal before processing of the cover sheet.